Charts Do Not Automatically Update When Data Changes

Question

Hopefully this is an easy one. I have a series of charts in MS Excel that point to data on the same worksheet. The data on the worksheet is calculated using a VBA function. W

Answer 1

I've found that calling this Sub works...

Sub DoAllEvents()
    DoEvents
    DoEvents
End Sub

BUT Microsoft cautions about being caught with the next DoEvents executing before the first DoEvents completes, which can happen depending on how often it's called without a delay between calls. Thus DoEvents appears to be acting as a type of non maskable interrupt, and nesting non maskable interrupts can cause the machine to freeze for multiple reasons without any recovery other than reboot.

(Note: If one is not calling the routine above, often and quickly, nesting may not be an issue.)

Using the following Sub below, which I modified from their suggestion, prevents this from happening.

Sub DoAllEvents()
    On Error GoTo ErrorCheck
    Dim i
    For i = 1 To 4000    ' Start loop. Can be higher, MS sample shows 150000
        'I've found twice is enough, but only increased it to four or 4000.
        If i Mod 1000 = 0 Then     ' If loop has repeated 1000 times.
            DoEvents    ' Yield to operating system.
        End If
    Next i
    Exit Sub
ErrorCheck:
    Debug.Print "Error: "; Error, Err
    Resume Next
End Sub

I appears that the number of DoEvents needed is based on the number of background tasks running on your machine, and updating the graph appears to be a background task for the application. I only needed two DoEvents because I call the routine frequently; however, I may end up upping it later if needed. I also keep the Mod at 1000 so to not change the lag between each DoEvents as Microsoft suggests, preventing nesting. One possible reason you might want to increase the number from 2000 to a higher number is if you system does not update the graph. Increasing this number allows the machine to handle larger numbers of background events that DoEvents might encounter through multiple calls as they are probably on a stack, and the DoEvents event is only allowed to run a specific number of cycles before marking its place in the stack to allow unhandled events and returning, leaving them to be handled on the next call. Thus the need for multiple calls. Changing this to their example of 150000 doesn't appear to slow the machine too much, to play it safe you might want to make it 150000.

Note: the first example Sub with two DoEvents is probably safe depending on how often you call the Sub, however, if called too often, your machine might freeze up. Your call. ;-)

PS: DoEvents will become one of your best calls if you create a lot of nested loops and the program doesn't behave as expected. Fortunately, this is available in all apps that use VBA!